Mold forming apparatus



Mwfih 1950 L. 1.. JOHNSTON mow FORMING APPARATUS Filed March 9, 1948INVE F1 Lc yal L Patented Mar. 7, 1950 HOLD FORMING APPARATUS a Loyal L.Johnston. Zelienople, 2a., aalirnor to Herman Pneumatic Company,Pittsburgh, Pm, a corporation of Pennsylvania Application March 9, 1948,Serial No. 18,171

This invention relates to mold forming apparatus and particularly toapparatus for forminl molds of molding material such as sand. r phiteand the like used in foundries. The invention has to do particularlywith the formation of hollow molds and the compacting and shaping of themold forming material at the inner surface of the mold.

While my invention is of general utility in the preparation of varioustypes of foundry moldsit is well adapted for use in forming hollow,generally cylindrical molds of sand or similar mold forming materialsuch as may be used for the casting of generally cylindrical products,for example, the centrifugal casting of pipe. Purely for purposes ofexplanation and illustration the invention will be described as embodiedin mold forming apparatus for the making of sand molds for thecentrifugal casting of cast iron soil pipe. The apparatus which is thesubject of the present invention may be embodied in molding machines ofthe type disclosed in my copending application Serial No. 643,318, nowPatent No. 2,449,900, granted September 21, 19%.

Apparatus for forming a hollow, generally cylindrical sand mold for thecentrifugal casting of soil pipe comprises a generally cylindricalhollow iiask which may be rotated both during formation of the sand moldand during centrifugal casting of the soil pipe, preferably atrelatively high speed during the latter period, the sand mold beingformed therein by introducing sand, rotating the flask and introducinginto the flask a former or mandrel whose function is to engage and pressagainst the sand to compact and shape the inner surface thereof, i. e.,the surface of the mold which is to contact the molten metal duringcentrifugal casting. In one method of procedure the sand is introducedinto the flask and the flash is rotated fast enough to cause the sand tocling to the inner surface of the flask, an axial hole through the sandthereby being formed. The former or mandrel may be introduced throughthe hole. Desirably a generally cylindrical mandrel is used. Duringintroduction of the mandrel it may be positioned coaxiaily with theflask and hence coaxially with the hole in the sand. After the mandrelhas been introduced its free end is preferably supported so that themandrel when ready for operation upon the sand is in the nature of abeam supported at both ends outside the flask.

The mandrel supports may be journals in which the mandrel is rotatabiymounted. The supports are movable transversely of the axis of the flaskClaims. (CI- 22-22) axis of the flask it compacts and shapes the sand toform in the flask a generally cylindrical hollow sand mold with itsinner surface smoothed and compacted and which is adapted for thecentrifugal casting of cast iron soil pipe. After the mold has beencompacted and shaped the mandrel may be returned to substantiallycoaxial position in the flask and may be withdrawn from the flask, afterwhich the flask may be provided with a core at one end and molten ironmay be introduced to form the soil pipe. The present invention hasnothing to do with the method employed in the centrifugal casting of thesoil pipe and it may be assumed that a conventional centrifugal castingmethod is employed.

One of the principal problems which has been encountered in the makingof soil pipe by centrif ugal casting has been that the pipe has not beenof uniform outside diameter, the outside of the pipe has not beenstraight and the wall thickness of the pipe has not been uniform. Thishas been due to the fact that the inner surface of the sand mold in theflask, i. e., the surface against which the molten metal formingtheoutside of the pipe freezes during centrifugal casting, has not beenstraight axially of the flask. Since that surface is formed by themandrel it follows that at the time of formation the mandrel has notbeen. straight. It has been found that the mandrel for forming the moldis subject to deflection and actually deflects when in use. When acylindrical mandrel is used which is supported at both ends and thatmandrel is pressed against the sand in the flask the mandrel deflects.the middle portion thereof being pushed back by the sand away from theflask. Thus although the mandrel when not in use may be straight it iscurved during the time when it is forming the mold. The result is thatthe inside diameter of the sand mold in which the pipe is cast issmaller at the middle portion of the mold than at the ends. This shapeis transmitted to the outside of the pipe and the undesirable resultsabove pointed out occur.

I have devised mold forming apparatus obviating the disadvantages aboveexplained. I provide mold forming apparatus comprising a flask ano es? 3adapted to contain a hollow body of molding material and a formerextending within the flask for compacting and shaping the inner surfaceof the molding material. the former being subject to deflection whenpressed against the molding material and being shaped so that whendeflected by being pressed against the molding material the surfacethereof in contact with the molding material assumes predetermineddesired conformation diflerent from its conformation when undeflectedwhereby to impart to the molding material a predetermined desired shape.When it is desired to form a cylindrical mold the former is designedwith its middle portion which engages the mold bulged outwardly when notunder deflection; when the former is in use under deflection its sandengaging surface will be approximately straight and a cylindrical moldwill be formed. If it is desired to form a mold which is of other thancylindrical shape the desired shape of the mold is ascertained and theformer is designed so that its mold forming surface differs from thedesired shape of the mold by the amount which it will deflect when inuse.

Other details, objects and advantages of the invention willbecome'apparent as the following description of a present preferredembodiment thereof proceeds.

In the accompanying drawings I have shown a present preferred embodimentof the invention in which Figure 1 is a diagrammatic axialcross-sectional illustration of a conventional flask and mandrel for theformation of a sand mold for the centrifugal casting of cast iron soilpipe;

Figure 2 is a view similar to Figure 1 but showing my improved mandreland the improved results obtained by its use; and

Figure 3 is an enlarged view of my improved mandrel but with a portioncut away.

. Referring first to Figure 1, there is shown a flask 2 which is ofgenerally cylindrical shape with a generally cylindrical bore 3 therein.the bore being enlarged at one end as indicated at 4 for the formationof a pipe bell. The flask itself may be of conventional design, beingdesirably of cast iron. Cooperating with the flask to form a mold ofsand 5 disposed within the flask is a former or mandrel 6. The mandrel 6when in use is mounted in bearings I and 8 at its respective ends sothat it may rotate in contact with with the sand. It has an enlargement9 within the portion 4 of the flask as is conventional. The mandrel alsohas a spigot forming enlargement H1. Between the enlargements 9 and Inthe mandrel is cylindrical.

The bearings l and 8 are mounted so that when the mandrel is in place inthe flask they may be moved in unison transversely of the axis of theflask to bring the mandrel into engagement with the sand to compact andshape the sand into a mold. In Figure 1 the direction of movement of thebearings 1 and 8 transversely of the axis of the flask is toward the topof the figure. The mandrel has been moved against the sand at the upperportion of the figure and the pressure of the slender mandrel againstthe sand has caused it to deflect or bend so that its central portion isdisposed farther from the upper inner surface of the flask than its endportions. The bending of the mandrel is indicated in Figure 1. Thisresults in the formation j' of a sand mold whose internal diameter issub.- stantially less in the region of its middle portion than at itsends. The disadvantages of the for- 4 mation of such a mold have beenexplained above.

Figure 2 shows a flask and mandrel made in accordance with my invention.The flask 2 and the bearings I and 8 may be the same as in Figure 1.However the mandrel 6' of Figure 2 is different from the mandrel 6 ofFigure l. The enlargements 9' and W of the mandrel II may be identicalwith the enlargements 9 and l 0 of the mandrel 8 but the portion of themandrel 6' between the enlargements 9 and I0 is not cylindrical. It isbulged adjacent its center, i. 8., the diameter of the mandrel at itscenter is substantially greater than its diameter adjacent its ends.

The mandrel 6' will deflect when in use but since it is made with itscenter bulged when not under deflection the surface of the mandrelengaging the sand will be substantially straight when the mandrel isdeflected and will result in the formation of a sand mold having asubstantially cylindrical inner surface.

While I have shown and described a present preferred embodiment of theinvention it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied within the scopeof the following claims.

I claim:

1. Mold forming apparatus comprising a flask adapted to contain a hollowbody of molding material and a former extending within the flask forcompacting and shaping the inner surface of the molding material, theformer being of small cross-section in relation to its length and hencebeing subject to deflection when in use, the mold engaging surface ofthe former being when undeflccted convexly curved in the longitudinaldirection so that when under deflection in use the portion of it inengagement with the mold will be substantially straight in thelongitudinal direction whereby to form a substantially straight mol 2.Mold forming apparatus comprising a flask adapted to contain a hollowbody of molding material and a former extending within the flask forcompacting and shaping the inner surface of the molding material, theformer being of small cross-section in relation to its length and hencebeingsubject to deflection when in use, the mold engaging surface of theformer being when undeflected bulged outwardly in the region of itsmiddle so that when under deflection in use the portion of it inengagement with the mold will be substantially straightened out wherebyto form a substantially straight mold.

3. Mold forming apparatus comprising a ro tatable flask adapted tocontain a hollow body of molding material and a forming mandrelextending within the flask for compacting and shaping the inner surfaceof the molding material upon rotation of the flask, the mandrel being ofsmall cross-section in relation to its length and hence being subject todeflection when in use, the mold engaging surface of the mandrel beingwhen undeflected bulged outwardly in the region of its middle so thatwhen under deflection in use the portion of it in engagement with themold will be substantially straightened out whereby to form asubstantially straight mold.

4. Mold forming apparatus comprising a rotatable flask adapted tocontain a hollow body of molding material and a forming mandrelextending within the flask for compacting and shaping the inner surfaceof the molding material upon rotation of the flask, the mandrel being ofsmall cross-section in relation to its length and hence being subject todeflection when pressed against the molding material, the mold engagingsurface of the mandrel being when undeflected bulged outwardly in theregion of its middle so that when pressed against the molding materialthe portion of it in engagement with the mold will be substantiallystraightened out whereby to form a substantially straight mold.

5. Mold forming apparatus comprising a flask adapted to contain a hollowbody of molding material and a slender elongated flexible formerextending within the flask for compacting and shaping the inner surfaceof the molding mateial, the former being subject to deflection whenpressed against the molding material, the surface of the former whichengages the molding material being, when the former is undeflected, ofconformation differing from the conformation of the mold to be formed byan amount such that when the former is deflected by pressing it againstthe molding material in formation of the mold the ortion of such surfacein engagement with the molding material will assume said conformation ofthe mold.

6. Mold forming apparatus comprising a rotatable flask adapted tocontain a hollow body of molding material and a slender elongatedflexible forming mandrel extending within the flask for compacting andshaping the inner surface of the molding material upon rotation of theflask, the mandrel being subject to deflection when pressed against themolding material, the surface of the mandrel which engages the moldingmaterial being, when the mandrel is undeflected, of conformationdiffering from the conformation of the mold to be formed by an amountsuch that when the mandrel is deflected by pressing it against themolding material in formation of the mold the portion of such surface inengagement with the molding material will assume said conformation ofthe mold.

7. Mold forming apparatus comprising a rotatable flask of generallycircular cross-section adapted to contain a hollow body of moldingmaterial and a slender elongated flexible forming mandrel of generallycircular cross-section extended through the flask and supported at bothends for movement transversely of its length relatively to the flask toengage, compact and shape the inner surface of the molding material uponrotation of the flask, the mandrel being mounted for rotation while inengagement with the molding material, the surface of the mandrel whichengages the molding material being, when the mandrel is undeflected, ofconformation differing from the conformation of the mold to be formed byan amount such that when the mandrel is deflected by pressing it againstthe molding material in formation of the mold the portion of suchsurface in engagement with the molding material will assume saidconformation of the mold.

8. A slender elongated flexible former for compacting and shaping theinner surface of molding material in a flask, the former being subjectto deflection when pressed against the molding material, the surface ofthe former which engages the molding material bsing, when the former isundeflected, of conformation differing from the conformation of the moldto be formed by an amount such that when the former is deflected bypressing it against the molding material in formation of the mold theportion of such surface in engagement with the molding mateial willassume said conformation of the mold.

9. A slender elongated flexible rotatable forming mandrel of generallycircular cross-section for compacting and shaping the inner surface ofmolding material in a flask, the mandrel being subject to deflectionwhen pressed against the molding material, the surface of the mandrelwhich engages the molding material being, when the mandrel isundeflected, bulged outwardly in the region of its middle so that whenthe mandrel is deflected by pressing it against the molding material information of the mold the portion of such surface in engagement with themolding material will be relatively straightened out.

10. Mold forming apparatus comprising a rotatable elongated open-endedflask adapted to contain a hollow body of molding material and formingmeans extending through the flask and supported at both ends of theflask for compacting and shaping the inner surface of the moldingmaterial upon rotation of the flask, said means being of smallcross-section in relation to the length thereof and hence being subjectto deflection when pressed against the molding material, the transversedimension of said means in the region of its middle being greater thanthe transverse dimension of said means adjacent the ends of the flask sothat when said means is pressed against the molding material the portionof the surface thereof in contact with the molding material will tend tostraighten out.

LOYAL L. JOHNSTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,504,497 Perry Aug. 12, 19242,187,250 Sendzimir Jan. 16, 1940 FOREIGN PATENTS Number Country Date688,270 France May 12, 1930

